A vibration damper assembly is generally utilized in a clutch driven plate assembly for a motor vehicle power train to control engine induced torsional vibration in the connected elements of the power train which will produce objectionable conditions, i.e. impact loads, pulsations, noises, etc. Circumstances sometimes occur which require a vibration damper having special characteristics to control objectionable vibration and/or gear rattle in the transmission or drive line which may occur at neutral idle or under engine full load. A damper with a straight line torque vs. amplitude curve will not always satisfy all conditions of use, therefore a damper may be required with a step-rate torsional spring characteristic having a very low initial rate, which progressively increases to provide a final torque requirement with a smooth transition from one step to the next.
In most current damper assemblies, torsional spring rates are generally high based on the required torque capacity and available amplitude. The increasing use of smaller engines and the desire to reduce engine idle rpm results in excessive transmission rattle at a low idle speed. Damper assemblies with an extremely low initial torsional spring rate and zero or minimal damping friction have been successful in reducing idle gear rattle, however, damping friction normally required to reduce vehicle driveline torsional vibrations is difficult to control in a damper which combines low and high torsional spring rates. The present invention provides novel damper arrangements to overcome the above-mentioned problems.